This invention relates generally to methods and apparatus for evaluating the tendency of sample bulk particulate solids to segregate by fluidization or exposure to permeation by gases. More particularly, it relates to apparatus for controlled fluidization of a vertical column of the solids by a gas such as air and subsequent collection of samples from separate segments of the column. The samples are suitable for conventional evaluation and comparison by screening, assays or other measurements to quantify the potential segregation by fluidization effects or gas entrainment.
Bulk solids generally comprise particles of different sizes. It is commonly desirable to maintain a uniform concentration of each size throughout the body during industrial processing, storage and packaging. However, segregation of the particles by size frequently occurs during processing steps such as the filling or discharge of a bin, tumble blending, pneumatic conveying and other gas assisted bulk solid handling processes. As a result of segregation by fluidization, different regions within a body of the solids comprise different proportions of fine and coarse particles and uniformity of the mixture is lost.
Vertical segregation frequently occurs, resulting in horizontal layers comprising differing proportions of fine and coarse particles. Fine particles generally have a lower permeability for gas than coarse particles and therefore tend to retain the gas longer. Thus for example, on filling a hopper the coarse particles tend to become more concentrated in the lower layers while the fine particles become more fluidized and tend to become concentrated in the upper layers. Similar effects occur after tumble blending if the solids are susceptible to fluidization. These effects are particularly noticeable in materials that contain a significant concentration of particles below 100 microns in size. Fluidization segregation is also likely to occur when fine materials are pneumatically conveyed, filled or discharged at high rates, or if gas counterflow is employed.
A principal object of this invention is to provide a test method and apparatus for precisely controlled fluidization of a sample body of particulate solids, followed by the separate retrieval of portions of the sample from different vertical levels of the fluidized body.
A second object is to provide apparatus that facilitates the retrieval of the segregated samples without disturbing the state of the samples.
A third object is to provide test apparatus adapted for improved containment of the sample solids during the test procedure. This is particularly desirable for the testing of very fine powders.
A further object is to provide apparatus adapted for accurately repeatable fluidization of successive samples, permitting greater reliability and accuracy in comparing the results of repeated test procedures on samples from the same body of bulk solid or from differing bodies of solids.
With the above and other objects hereinafter appearing in view, this invention provides apparatus for obtaining samples of bulk particulate solids from a columnar sample chamber containing fluidized particulate solids, for evaluating their sensitivity to segregation by fluidization. The apparatus includes a plurality of stacked discs rotatably mounted on a vertical shaft. The discs are provided with bores that are alignable to form a columnar sample chamber comprised of segments each to be separately collected. The discs are also provided with apertures for supporting sample jars, and the discs are independently and sequentially rotatable to cause the segment of the segregated sample solids within the bore of each disc to be separately deposited in a sample jar.
Means are provided to compress the discs during fluidization, thus minimizing leakage. When the discs are being rotated the compression force is reduced.
Other features, as hereinafter described, are employed to provide a compact apparatus in which the fluidization is precisely controlled for uniformity in repeated tests, thus increasing the reliability of evaluation procedures for comparing the results of separate samplings of the same or different solids.